Crank case scavenged, cylinder ported two-stroke cycle engines of the prior art are commonly used for a wide variety of light duty applications. Two-stroke cycle engines of the prior art, however, have several shortcomings.
One shortcoming arises from the fact that prior art two-stroke cycle engines typically have intake and exhaust ports at about the same level. This results in some of the intake fuel-air mixture following the exhaust out of the exhaust port, thereby decreasing efficiency and increasing emissions.
Another shortcoming of prior art two-stroke engines arises because some of the engine's lubricating oil can pass to the exhaust port, thus producing emissions and often leaving deposits on the walls of the exhaust port, thus forming a hard carbon layer or “coking” which restricts the exhaust and causes other problems.
Yet another shortcoming of prior art two-stroke cycle engines involves the difficulty of bringing intake fuel-air mixture from the bottom of the engine cylinder to the top of the cylinder where the igniter is located. During part throttle operation, most of what remains in the cylinder are burnt gases. Moving the small amount of fresh intake mixture undiluted by burnt gases to the igniter becomes very problematic. Misfires are typical, resulting in irregular operation, and surging. Various arrangements, such as loop scavenging or deflecting pistons, have been suggested for passing the mixture to the combustion chamber without some of it escaping via the exhaust port. None of these various arrangements, however, have been wholly successful.
Yet another shortcoming of prior art two-stroke cycle engines involves the difficulty of lubricating the cylinder wall and piston. Having the piston pass over both intake and exhaust ports around the lower circumference of the cylinder limits the amount of oil that can be delivered to the upper cylinder wall. Piston thrust against the cylinder wall then results in scuffing and premature wear.
Yet another shortcoming of prior art two-stroke cycle engines involves the use of the crank case as the delivery pump for the scavenge charge. This results in delivery of the charge at very limited pressure, limiting control of the scavenge process. Mixing oil with the fuel or an expensive oiling system is also required, as are more expensive bearings that will survive on oil vapor only.
Fuel injection systems have been utilized in order to reduce emissions and to delay fuel injection until an exhaust port is closed. However, such systems are generally costly and often involve new problems.
For many years, efforts have been made to deliver a fresh fuel-air charge directly to a spark plug to insure ignition with every piston stroke. None of these efforts, however, have been truly successful.
Accordingly, there is a need for a two-stroke cycle engine which avoids the aforementioned problems in the prior art in an efficient and inexpensive manner.